Quartz Types, Composition and Forms

Quartz Gemstones in Nature
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What is Quartz?

Quartz is the second most abundant mineral in earth’s crust, after feldspar. It is a hard, crystalline mineral made of silica (silicon dioxide). The chemical formula of quartz is SiO2, with the atoms linked in a continuous framework of SiO4 (silicon-oxygen tetrahedra); each oxygen is shared between two tetrahedra. .

It is found in igneous, sedimentary and metamorphic rocks. It has high resistance against weather changes and works as a cementing agent in sedimentary rocks.

Forms of Quartz

Quartz is found in two forms; α-quartz & β-quartz. Both forms are chiral. β-quartz is often referred to as high-temperature quartz, and α-quartz is known as low-temperature quartz. α-quartz is converted to β-quartz at the temperature of 573 °C (846 K; 1,063 °F). A substantial volume change accompanies the transformation process; it often breaks ceramics or rocks passing through this temperature threshold.

Quartz is colorless and transparent in pure form. The presence of impurities often makes it colored and alters its properties.

Different types of Quartz

Physical Properties

Quartz is used in so many industries owing to its physical properties. It is a hard, durable, and economically valuable mineral. Quartz’s physical properties are summarized below.

  • Chemical classification: Silicate
  • Color: It occurs in a variety of colors; pure quartz is white
  • Luster: Vitreous
  • Streak: Colorless
  • Diaphaneity (ability to transmit light): Transparent to translucent, can be opaque
  • Cleavage: None, usually breaks with a conchoidal fracture
  • Specific gravity: 2.6 – 2.7
  • Mohs Hardness: 7
  • Crystal system: Trigonal
  • Diagnostic properties: Glassy and shiny luster, hard, and breaks with a conchoidal fracture

Where is Quartz Found?

Quartz is present in substantial amounts all over the world. It is found in all three types of rocks; sedimentary, igneous and metamorphic. Moreover, it is highly resistant to weathering changes; therefore, its occurrence is not limited.

It is also extremely durable against mechanical and chemical weathering. Hence it can be found in mountains, beaches, rivers, and desert sand.

Types of Quartz

Quartz is usually classified based on its microstructure and color. Let’s go through both classification systems.

According to Microstructure

The scientific classification is based on the microstructure of the mineral. Color is a secondary identifier for quartz and other microcrystalline minerals. There are 18 varieties of quartz according to this system.

  • Agate: It is multi-colored and has curved or concentric banded chalcedony with a semi-translucent to translucent appearance.
  • Amethyst: It is purple to violet with a transparent appearance.
  • Ametrine: It is a mix of amethyst & citrine with purple to orange/brown hues with a transparent appearance.
  • Aventurine: It has aligned inclusions with a translucent to opaque appearance.
  • Carnelian: It has a translucent appearance with reddish-orange chalcedony.
  • Chalcedony: It occurs in many varieties.
  • Citrine: It is usually yellow colored with orange, reddish, brown, and greenish-yellow hues with a transparent appearance.
  • Dumortierite quartz: It contains large amounts of blue dumortierite crystals with a translucent appearance.
  • Herkimer diamond: It is colorless with a transparent appearance.
  • Jasper: An opaque variety that is usually red to brown and has an opaque appearance.
  • Milky quartz: White quartz with a translucent to opaque appearance.
  • Onyx: It is multi-colored with straight banded chalcedony with a semi-translucent to opaque appearance.
  • Prasiolite: It is transparent and green.
  • Rock crystal: It is transparent and colorless.
  • Rose quartz: It is usually transparent with a pink appearance.
  • Rutilated quartz: Rutilated quartz contains needle-like inclusions of rutile.
  • Smoky quartz: It is transparent to opaque, gray in color with a brownish hue.
  • Tiger’s eye: It is chalcedony with fibrous gold, red-brown, or a bluish-colored color.

According to Color

Pure quartz, also known as clear quartz or rock quartz, is colorless, transparent, or translucent. The color difference in quartz is due to the presence of impurities. Here is a list of commonly available color quartz.

  • Amethyst: The color ranges from shiny bright violet to dull lavender. Its biggest deposits are found in Mexico, Brazil, Russia, Moroccan, and France.
  • Blue Quartz: It contains inclusions of fibrous magnesio-riebeckite or crocidolite.
  • Dumortierite quartz: It has a silky appearance with a blue hue. Some varieties also display shades of purple or gray. Blue quartz is considered a minor gemstone.
  • Citrine: Its color ranges from pale yellow to brown. Natural citrines are rarely found.
  • Milky quartz: It is the most common variety of quartz with a cloudy or milky appearance due to gas or liquid inclusions when the crystal is formed.
  • Rose quartz: It has a pink to rose red hue due to the presence of iron, manganese, or titanium in trace amounts.
  • Prasiolite: It is also known as vermarine with a green color. Almost all natural prasiolite comes from Brazil. However, its reserves are also located in Poland and Canada. Prasiolite is rare; most green quartz is heat-treated amethyst.

Quartz Uses

Quartz is used in various industries. Its durable properties make it one of the most useful naturally occurring materials. Its major uses are outlined below.

  • Sedimentary sands made up of 100% quartz are used in glass products like fiberglass, specialty glass, container glass, and flat plate glass.
  • Quartz has a hardness of 7 on the Mohs scale, making it more durable and powerful than other materials. This property allows it to be used as an abrasive.
  • Quartz sand is used in sand blasting, scouring cleaners, grit papers, and as a grinding media.
  • Quartz is used as foundry sand because it is resistant to chemicals and heat.
  • Refractory bricks are made from sand because of their high heat resistance.
  • Quartz is also used in the petroleum industry for hydraulic fracturing of oil and gas wells.
  • It is also used as filler in paint, rubber, and putty manufacturing.
  • Quartz is used in watches and other timekeeping instruments.
  • Quartz is used as a gemstone. Natural quartz is rare, and its vibrant colors make it an excellent jewelry piece.

Synthetic Grown Quartz

Quartz demand has outgrown its natural production. The need was first felt during World War II, and private and government-owned industries started working on producing synthetic quartz. Today, most quartz is produced synthetically in laboratories to meet the demand.

The manufactured quartz crystals can be grown in different shapes, sizes, and colors to satisfy the purpose for which it is being built.

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